As a sealant for solid oxide fuel cells (SOFC), crystallized glass has been proposed, with which, however, there has been a problem that deterioration in sealing performance occurs when exposed to high temperatures for an extended period of time, due to partial transformation or melting of the precipitated crystals.
In particular, there has been a problem that when exposed to high temperatures of 970° C. or over, cracks are formed in the crystallized glass, which brings about deterioration of the sealing performance, due to partial melting of precipitated crystals leading to a change in its thermal expansion coefficient and loss of linearity of the thermal expansion coefficient.    [Patent Document 1] Japanese Patent Application Publication No. 2007-161569